A disk rotor is made of cast iron containing graphite and includes a sliding ring part which has a circumferential outer surface and a circumferential inner surface. A sliding surface is formed between the circumferential outer surface and the circumferential inner surface of the sliding ring part. Graphite functions as a solid lubricant or to damp vibration, so that it can be effectively used to enhance the performance of the disk rotor. In the disk rotor, because the sliding surface of the sliding ring part comes into frictional contact with a relative member when braking, it is necessary to reduce partial abrasion with respect to the circumferential direction.
A representative method for casting a disk rotor using cast iron was proposed. (Patent Literature No. 1.) As shown in FIG. 16, a mold 5X used in this conventional method has a casting cavity 53X which forms a sliding ring part and has an annular shape, an outer circumference forming surface 531X which forms the circumferential outer surface of the sliding ring part and has an annular shape, and an inner circumference forming surface 532X which forms the circumferential inner surface of the sliding ring part and has an annular shape. Furthermore, gates 61X, 62X and 63X are formed in the outer circumference forming surface 531X of the mold 5X at positions spaced apart from each other at regular intervals with respect to the circumferential direction. In addition, runners 71X, 72X and 73X respectively communicate with the gates 61X, 62X and 63X. Here, the gates 61X, 62X and 63X are respectively oriented in the directions parallel to normal lines 77X, 78X and 79X passing through a central axis P5 of the casting cavity 53X in the radial directions.    Patent Literature No. 1: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2007-211828